Conventionally, roofs or roof decks of buildings and the like are commonly covered with so-called tar paper which, in turn, is covered with either shingles or is hot-mopped with tar. Since hot-mopping requires considerable labor, is relatively dangerous and difficult to perform and, cannot be done when the ambient temperature is too low, attempts have been made to find a substitute to eliminate or reduce such procedure.
Sheets of asphalt have been used by heating the sheets and laying them upon the roofing surface in overlapping relationship. This can eliminate the necessity of the step of applying a hot-mopping coating since the asphalt itself can form the roofing surface. However, the heating step used involves manually directing a torch against the lower surface of the asphalt sheet until it sufficiently melts or softens so that it can be applied against the roof surface and the overlapped portion of the adjacent sheet for adhering thereto. Since sheets of asphalt are relatively fragile to handle, such sheets have been made of upper and lower layers with a reinforcing fabric layer between them, thus forming a three layer lamination.
In using asphalt sheets, whether of single ply or of the laminated type, the application of heat to the surface of the lower layer must be performed very carefully. That is, insufficient heat will not uniformly soften the surface so as to obtain a uniform adherence to the overlapped surfaces. Areas where the sheet is not properly adhered can later blister or bubble. Conversely, the application of too much heat, particularly localized excessive heat where the torch is not moved carefully or swiftly enough so as to cause its flame to overheat a particular area, causes the asphalt to become runny and drip, thus ruining the lower layer and simultaneously heat softening and melting the upper layer. When this overheating occurs the integrity of the sheet is affected, i.e. the upper layer is thinned or holed or otherwise adversely affected. This adverse effect usually cannot be visually determined, particularly during the necessarily rapid movement of the workmen in heating and applying the sheets at awkward locations.
Because of the problems resulting from heat damage to the sheets, another form of sheet proposed for roofing is formed of a plastic material, such as synthetic rubber of suitable chemical composition. These sheets are applied by means of utilizing an adhesive so as to form an adhesively secured, continuous, water impervious sheet covering for the roof. However, there are disadvantages in utilizing adhesive securing means since the adhesive itself can be applied only where the temperature is in the relatively warm range and the uniformity of the adhesive coating upon the lower surface of the sheet is not easily obtained in the working conditions involved in applying the material upon a roof surface. In contrast, the heat softening technique used with the asphalt sheets can be utilized even during cold weather. That lengthens the season for roofing work and in addition, makes it possible to do repair work regardless of season.
Further, the rubber types of materials available are relatively expensive to purchase and use. Likewise, the adhesives required are also relatively expensive and as in the case of using any adhesive in an outdoor, variable weather environment, there are difficulties in obtaining a good, uniform application.
There is presently available commercially a type of synthetic plastic material known as ethylene vinyl acetate or "EVA" which is used as sound deadening sheet material in automotive applications and for backing material for automotive carpets. The material itself is formed in sheets by extruding it directly upon a substrate, such as a previously woven automotive carpet, or by extruding or calendering it as unsupported film or sheet which is then used in sheet form for lining areas to be sound deadened or protected. Examples of such use are within the side panels, door panels or interior roofing areas of the automobile metal body.
The specific compositions of such sheet material is varied considerably depending upon the quality, expense, available raw materials and the like. In addition, the basic ethylene vinyl acetate copolymer may be "filled" with substantial amounts of calcium carbonate, e.g. limestone, or clay or other inexpensive, readily available materials. The amounts of filler can be enhanced by adding oils to the blend which thus permit the formation of a usable mixture of plastic and filler which is relatively inexpensive and yet forms a monolithic, water impervious sheet.
The invention herein does not relate to the chemical composition or the technique for forming the sheet, all of which is known to those skilled in the art. A description of this type of material, which is commercially available from such suppliers as E. I. DuPont Denemours Company of Wilmington, Del., is found in DuPont's U.S. Pat. No. 4,191,791 issued Mar. 4, 1980 to Schumacher and entitled "Highly Filled Thermoplastic Compositions Based Upon Ethylene Interpolymers and Processing Oils". Such patent discloses various compositons and blends utilizing EVA with varying amounts of fillers such as clay, calcium carbonate and the like. The disclosure in such patent, which is relatively lengthy, is included herein by reference.
Other disclosures of the commercially available types of ethylene vinyl acetate copolymer sheets or materials which can be formed into sheets are found in the patent to Schwartz, U.S. Pat. No. 3,904,456 issued Sept. 9, 1975 which discloses a film or sheet having a sixty to ninety percent by weight inorganic filler material and useful for sound blocking purposes or as a sound blocking backing on carpets. Another disclosure is found in the patent to Gladding, U.S. Pat. No. 3,817,893 issued June 18, 1974. This patent describes an unfilled material having oil and wax additives and useful for sound attenuation.
Still another patent to Sands, U.S. Pat. No. 3,390,035 issued June 25, 1968, discloses the backing of tufted carpets with ethylene vinyl acetates applied as a hot melt. The composition includes an inert filler such as clay, calcium carbonate, silicon, etc. up to about fifty percent. An even earlier patent to Boier, U.S. Pat. No. 3,010,899 issued Nov. 28, 1961, discloses a ethylene vinyl acetate copolymer to which a clay filler is added, for use as an automobile undercoating.
The EVA materials, can be produced in sheet form to provide an inert sound attenuating, monolithic, water impervious surface. Thus, the invention herein relates to the utilization of such EVA material combined with asphalt, so as to obtain the advantages and economies of each and an overall improvement due to the coaction between them, for a roofing material or the like.